Catalytic dehydrogenation of hydrocarbons



Patented June 1-1 1940 U ITED I STATES PATENT Fl es osrsnvrrc nsnynnocsmmon or a nrnnoosnsons No Drawing. Application December s1, roar, Serial No. 182,808

12 claims. (or. 2oo-csa) I This invention is concerned with reactions involving the dehydrogenation of aliphatic hydrocarbons and refers more specifically to the pro.- I

' duction of cyclic hydrocarbons by reactions in- 6 volving the dehydrogenation of parafllnic hydro-- carbons containing at least six carbon atoms in straight chain arrangement to produce aromatics.

The process is therefore primarily applicable to normally liquid aliphatic hydrocarbon materials 10 consisting either of pure compounds or mixtures. y In the ordinary thermal treatment of aliphatic hydrocarbons; it is apparentthat the primary reactions involve a loss of hydrogen with the formation of mono-olefins and that further conversion involves a further loss of hydrogen and iormsidiolefins and miscellaneous cyclic hydrocarbons possibly resulting from the condensation and cycling of highly unsaturated aliphatic residues. In such cracking reactions, however, there is a considerable spread in the products which include normally gaseous hydrocarbons and liquid hydrocarbons running from the very lightest which can exist as liquid under ordinary conditions upto high boiling condensation products and tars. Under intensive cracking'conditlons there will be produced definite yields of aromatic hydrocarbons such as benzene and toluene although these yields are seldom high enough to make this method aromatic production one of 30 commercial importance. The present process deals with'the application or specific catalysts to the production of aromatics from aliphatic hydrocarbons, including both paraflns and mono-oi. a

In one specific embodiment the present invention comprises a process for the manufacture of aromatic hydrocarbons by subjecting the vapors of aliphatic hydrocarbons containing at least six' discussed are included in the generic term or "dehydrocyciiaation" and are typified by the reac-- tions shown below in which formation; of ben- 50 zene, toluene. and xylene from normalhexananormal heptane, and normal octane are shown.

CH: CH 0%: \CHI 0% CH H: CH on Ali cn, on

n-hexaue benzene on. c-cm 1 Cfib \CHr-CHa C? CH g. n, on, on Els a C a CH n-heptsno toluene on; on C CH CH Cg C0Ea I -o +4Hs CH CHr-CHr H t -CHa 0 i e c n-octane o-xyleno hydrogenation ot'the original molecule. Under the preferred conditions of operation, conditions are so regulated that maximum yields of the aromatic hydrocarbons are obtained. It is evident from theabove structural equations which have been substantiated by experimental work that end methyl groups of compounds having more than 6 carbon atoms in straight chain arrangement appearin the'benzene'ring. With higher molecular weight parafllns containing more than eight carbon atoms instraight chain arrangement, the reactions ordinarily become more complex, and with hydrocarbons from 10 to 12 carbon atoms in linear arrangement there is some. tendency for the formation)! naphthalene, The catalysts which are".used according to the present invention tobring. aboutdehydrogenation and cyclization of aliphatic hydrocarbons comprise, as already stated, mixtures of" aluminum oxide; chromium sesquioxide, and re:-

duced nickel. The proportions of these ingredients may be varied considerably though in general the aluminum oxide will be in major proportion and the chromium oxide and nickel in minor proportion. An eilective catalyst whose preparation will be described in a succeeding paragraph consists of approximately 65% by weight of aluminum oxide (A1203), .by weight of chromium sesquioxide (CraOa) and 5%- reduced nickel. .The relative proportions of the chromium oxide and the'reduced nickel may be varied somewhat depending upon the hydrocarbon treated to produce optimum yields of arcmatics. As a rule the amount of nickel present on the catalyst will be substantially less than the amount of chromium oxide and the total amount of nickel will be definitely a minor amount of the total weight of the catalyst. Y

The preferred catalysts are prepared by a special and specific procedure which may be briefly summarized as follows. An aqueous solution containing the nitrates of chromium and aluminum in proper; relative proportions for producing a catalyst containing the alumina and chromia in the proper ratio is treated with an alkali metal hydroxide such as sodium hydroxide to first precipitate the hydroxides of aluminum and chromium. These hydroxides are then redissolved in just the requisite excess of alkali to form a clear solution which will then comprise sodium aluminate, and sodium chromite. To

this solution a composite solution containing nickel nitrate and either ammonium nitrate or nitric acid is added to form a mixed precipitate of nickel, chromium, and aluminum hydroxides. The precipitate is washed with water to the removal of substantially all adsorbed salts and then dried and reduced in a current of hydrogen at gradually increasing temperatures up to 425-450 the eifect of small additions of nickel is to greatly accentuate the dehydrogenating properties of alumina-chromia mixtures so that dehy-- drocyclization reactions are effected at lower temperatures than when employing chromium oxides alone, alumina-chromia catalysts alone, or reduced nickel alone or on supports such as alumina.

In operating to produce aromatics from parafllns or mono olefins according to the present process, the granular catalystsconsisting of partlcles of an approximate mesh of-from 4 to 20 are placed incatalyst chambers and the vaporized aliphatic hydrocarbon is passed "through 1 the granular mass at temperatures of the order of from 400 to 500 C. which is considerably lower than those which are generally used with oxide catalysts or those comprisingaluminapr other refractory oxides promoted by lower oxides of ,metals such as chromium. The pressures employed are substantially; atmospheric and the rates .will be varied in accordance with the type of hydrocarbon undergoing treatment the character of the aromatic products desired. The products from the treatment will include fixed gases of which a large portion will be hydrogen,

a certain amount of low boiling hydrocarbons,

some olefins including'both mono and di-olefins, and preponderating'amounts of aromatics when conditions have been suitably chosen for the con-. version. .The aromatic products may be separated irom unconverted aliphatic hydrocarbons and the latter returned for further conversion in admixture with fresh charge.

The following example is given of the formation of aromatics from normal parafilnic hydro-e carbons to show the value of the process in comparison with other processes having the same object, although not with the intent of unduly circumscribing the scope of theinvention.

The catalyst for the reaction was prepared as follows. An aqueous solution containing 175 parts by weight of chromium nitrate,

CriNOg) 3.91120 and 375 partsby weight of aluminum nitrate,

was treated with an aqueous solution of sodium hydroxide to primarily precipitate the hydroxides of aluminum and chromium andthen redissolve the primary precipitate to form a solution of sodium aluminate and sodium chromite. To the clear solution, 35 parts by weight of nickel nitrate and 400 parts by weight of ammonium nitrate'in joint solution were added slowly with stirring to form a .mixed precipitate ofnickel,

' chromium, and aluminum hydroxides. The precipitate was washed by decantation and mechanical filtration, dried at a temperature of 110 C. and finally reduced in a current'of hydrogen at gradually increasing temperatures from about 200 to 450 C. The granulation of the material was effected after the drying stage and before reduction.

Using the catalyst prepared as above which comprised approximately 65% by weight of aluminum oxide, 30% by weight of chromium sesquioxide, and 5% nickel, normal heptane was vaporized and passed over the granular catalyst at a temperature of 450 C. The-vapors were preheated to this temperature, and the temperature of the catalyst bed was maintained by exterior heating on account of the endothermic character of the reaction. In a single pass through this catalyst the total liquid recovery was 62% by volum'e, the yield of toluene based on the charging material was 31% and the yield of oletlns (principally a mixture of heptenes) was 10.3%. Using a catalyst comprising 70% by weight of alumina and 30% by weight of chromium sesquioxide without nickel the liquid'recovery at the same temperature of 450 C. was 75%, the yield of toluene based on the charge was 24%, andthe yield of heptenes was 9%. It is thus seen that the use of nickel in conjunction with chromium sesquioxide gives definitely increased yields of toluene over the yields obtained when employing 'jalumina-chro'mia catalysts without nickel.

The

increased activity of the alumina-chromia-nickel catalyst is also shown by the lower liquid recovery indicating a higher degree of gasiilcation.v

The nature of the present invention is apparent from the foregoing specification including both descriptive and numerical sections neither oi' which is intended to bev unduly limiting.

I claim as my invention:

1. A process for dehydrogenating aliphatic -hydrocarbons which comprises subjecting the same to dehydrogenating conditions in the presence of a catalyst comprising a major proportion of alumina and minor proportions of chromium sesquioxide and nickel.

2. A process for dehydrogenating paramnic hydrocarbons which comprises subjecting the same to dehydrogenating conditions in the presence of a catalyst comprising a major proportion of alumina and minor proportions of chromium sesquioxide and nickel.

3. A process for dehydrogenating mono-olei'inic hydrocarbons which comprises subjecting the same to dehydrogenating conditions in the presence of a catalyst comprising a major proportion of alumina and minor proportions of chromium sesquioxide, and nickel.

4. A process for dehydrogenating aliphatic hydrocarbons which comprises subjecting the same to dehydrogenating conditions in the presence of a catalyst comprising a major proportion of alumina and minor proportions of chromium sesquioxide and nickel, the sesquioxide being in greater weight than the nickel.

5. A process for dehydrogenating parailinic hydrocarbons which comprises subjecting the same to dehydrogenating conditions in the presence or a catalyst comprising a major proportion of alumina and minor proportions of chromium sesquioxide and nickel, the sesquioxide being in greater weight than the nickel.

6. A process for dehydrogenating mono-oleiinic hydrocarbons which comprises subjecting the same to dehydrogenatingconditions in the presence of a catalyst comprising a major proportion of alumina and minor proportions of chromium sesquioxide and nickel, the sesquioxide being in greater weight than the nickel.

7. A process for producing aromatics from allphatic hydrocarbons of atleast six carbon atoms a in straight chain arrangement, which. comprises drogenating and cyclicizing conditions in thesubjecting the aliphatic hydrocarbons .to dehy- 8. A -process for producing aromatics irom paraflinic hydrocarbons of at least six carbon atoms in straight chain arrangement, which comprises subjecting the paraflinic hydrocarbons to dehydrogenating and cyclicizing conditions in the presence or a catalyst comprising a. major proportion of alumina and minor proportions of chromium sesquioxide and nickel.

, 9. A process for producing aromatics. mono-oleflnic hydrocarbons of at least six carbon atoms in straight chain arrangement, which comprises subjecting the mono-olefinic hydrocarbons to dehydrogenating and cyclicizing conditions in the presence of a catalyst comprising a major proportion of alumina and minor proportions of chromium sesquioxide and nickel. 10. A process for producing aromatics from aliphatic hydrocarbons of at least six, carbon atoms in straight chain arrangement, which comprises subjecting the aliphatic hydrocarbons to dehydrogenating and cyclicizing conditions in the presence of a catalyst comprising a major from proportion of alumina and minor proportions of chromium sesquioxide and nickel, the sesquioxide being in greater weight than the nickel.

' 11. A process for producing aromatics from parafllnic hydrocarbons of at least six carbon atoms in straight chain arrangement, which comprises subjecting the paraflinic hydrocarbons to dehydrogenating and cyclicizing conditions in the presence of a catalyst comprising a. niajor proportion of alumina and minor proportions of tions in the presence oi a catalyst comprising a major proportion of alumina and minor proportions of chromium sesquioxide' and nickel. the

sesquioxide being in greater weight than, the

nickel. v

VASILI KOMAREWSKY. 

